JP2010089542A - Pneumatic tire - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a pneumatic tire capable of suppressing its diameter growth and excellent in belt durability. <P>SOLUTION: The pneumatic tire has a belt arranged in such a manner that cords are inclined with respect to a tire circumferential direction; wherein, with a region making up 50 to 80% of a belt width around a tire equator line C defined as a mediate region Me, a region inward of the mediate region Me in a tire width direction defined as a center region Ce, and with a region outward of the mediate region Me in the tire width direction defined as a shoulder region Sh, cord angles of the belt 5 with respect to the tire circumferential direction are set such that a relation of θc>θs>θm is satisfied, where a cord angle in the mediate region Me is θm, a cord angle in the center region Ce is θc, and a cord angle in the shoulder region Sh is θs. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a pneumatic tire including a belt disposed such that a cord is inclined with respect to a tire circumferential direction.

  Conventionally, as an internal structure of a pneumatic tire used for heavy-duty vehicles such as trucks and buses, a structure in which a reinforcing belt is disposed on the outer peripheral side of a carcass that is a skeleton of a tire is known. The belt is usually disposed such that the cord is inclined at a predetermined angle with respect to the tire circumferential direction, and the cord angle is constant throughout the tire width direction.

  However, the cord angle of the belt may change non-uniformly through the vulcanization molding process (Patent Document 1 below). This is because the cord angle with respect to the tire circumferential direction of the belt becomes larger at both end portions than in the central portion in the tire width direction in accordance with the operation of changing the diameter of the tire and bringing it into close contact with the mold. As a result, at both ends of the belt, the number of ends (the number of cords per unit width) tends to be small and the binding force tends to decrease.

  FIG. 7 is a conceptual diagram showing a belt in which the cord angle is changed as described above. Symbol C is the tire equator line, and symbol W is the belt width (half of the belt is shown). A broken line is a virtual line when the code angle is constant. The cord angle θ with respect to the tire circumferential direction increases as the distance from the tire equator line C increases, and becomes maximum at the end of the belt. For this reason, the binding force of the belt is relatively lower at the end than at the center.

  By the way, a pneumatic tire changes in the direction in which a radial dimension becomes large by being filled with internal pressure or repeatedly traveling. This change is called radial growth. As the diameter growth proceeds, the shape retention of the tire is impaired and the uniformity is reduced, causing uneven wear. Therefore, it is desirable to reduce the diameter growth as much as possible, and for that purpose, it is important to secure the restraining force of the belt.

  In order to solve this diameter growth problem, a pneumatic tire is proposed in which the cord angle with respect to the tire circumferential direction of the belt is set to be large at the center in the tire width direction, small at both ends, and medium at the middle ( Patent Document 2) below. This is based on the knowledge that the diameter growth in the shoulder region is the most remarkable, and the cord angle around the end of the belt is adjusted to increase the binding force.

However, it has been found that such a tire does not have a sufficient effect of suppressing the diameter growth as described later, and there is still room for improvement. In addition, the end of the belt with a relatively small cord angle tends to increase the distortion, and the belt durability tends to decrease. For this reason, a pneumatic tire that can exhibit excellent belt durability while further suppressing the tire diameter growth is desired.
JP 2007-84035 A JP 2003-48111 A

  This invention is made | formed in view of the said situation, The objective is to provide the pneumatic tire which can suppress the diameter growth of a tire and was excellent also in belt durability.

  The present inventor has conducted extensive studies to achieve the above object, and has found the following matters. That is, when filling the tire with a high internal pressure or overlapping running, the sidewall portion having a relatively short carcass length has a small growth (bulge) outward in the tire width direction, as shown in FIG. A force F that pulls the shoulder portion located at the outer peripheral end inwardly acts. Therefore, when the diameter growth proceeds, the inner surface shape of the tire becomes convex toward the tire outer periphery side (the inner diameter is large) in the mediate region, and the tire shape tends to be non-uniform.

  Accordingly, it has been found that, even though the belt restraining force is low at the end of the belt, the mediate region should be treated rather than the shoulder region in order to more appropriately suppress the radial growth. Just by reducing the cord angle at the end of the belt as in the prior art, the effect of suppressing the diameter growth is not sufficient, the inner surface shape of the tire is not stable, and the problem of belt durability as described above also occurs. The present invention has been made on the basis of such knowledge, and can achieve the above object with the following configuration.

  That is, the pneumatic tire of the present invention is 50 to 80% of the belt width centering on the tire equator line in a pneumatic tire including a belt disposed so that the cord is inclined with respect to the tire circumferential direction. The region is a mediate region, the region inside the tire width direction from the mediate region is a center region, the region outside the mediate region in the tire width direction is a shoulder region, and the cord angle with respect to the tire circumferential direction of the belt, When the chord angle in the mediate region is θm, the chord angle in the center region is θc, and the chord angle in the shoulder region is θs, the relationship θc> θs> θm is satisfied.

  In the pneumatic tire according to the present invention, the cord angle of the belt with respect to the tire circumferential direction is minimized in the mediate region, and the restraint force of the belt is highest in the mediate region where the inner surface shape of the tire tends to change locally. I am doing so. In addition, the cord angle of the shoulder region is made smaller than that of the center region. Thereby, diameter growth can be suppressed uniformly over the whole tire width direction. Moreover, since the cord angle of the belt can be set relatively large in the shoulder region, an increase in distortion at the end of the belt can be suppressed, and excellent belt durability can be exhibited.

  In the above, it is preferable that the cord angle of the belt is gradually changed from the mediate region toward the center region while satisfying the relationship of θc−θm ≦ 5 °. This facilitates the smooth arrangement of the belt cord and ensures the belt strength appropriately. That is, when θc−θm> 5 °, a change in the cord angle becomes large, so that the smooth arrangement of the cord tends to be difficult. If the cord is bent, the belt strength may be adversely affected. is there.

  In the above, it is preferable that the cord angle of the belt is gradually changed from the mediate region toward the shoulder region while satisfying the relationship of θs−θm ≦ 3 °. This facilitates the smooth arrangement of the belt cord and ensures the belt strength appropriately. That is, when θs−θm> 3 °, a change in the cord angle becomes large, so that the smooth arrangement of the cord tends to be difficult. If the cord is bent, the strength of the belt may be adversely affected. is there.

  The present invention is particularly useful for a tire having an aspect ratio of 70% or less. In a tire with such a low flatness ratio, the length of the carcass in the sidewall portion is relatively short, and the bulge to the outside in the tire width direction is suppressed, and the change in the inner surface shape in the mediate region becomes significant. The configuration of the present invention is particularly useful.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a half sectional view of a tire meridian schematically showing an example of a pneumatic tire according to the present invention. The pneumatic tire includes a pair of bead portions 1, a sidewall portion 2 extending from the bead portion 1 to the tire outer peripheral side, and a tread portion 3 connected to each tire outer peripheral side end of the sidewall portion 2. The bead portion 1 is provided with an annular bead core 1a formed by covering a converging body such as a steel wire with rubber and a bead filler 1b made of hard rubber.

  The carcass 4 is disposed so as to be bridged between the bead portions 1 and is locked in a state where its end is wound up via the bead core 1a. The carcass 4 is constituted by a cord extending at an angle of approximately 90 ° with respect to the tire equator line C. As the cord, a steel cord and organic fiber cords such as polyester, rayon, nylon, and aramid are preferably employed. .

  A belt 5 is disposed on the outer periphery of the tread portion 3 of the carcass 4 to reinforce the carcass 4 by an effect. The belt 5 is constituted by a belt ply in which a large number of cords are topped with rubber, and the cords are disposed so as to be inclined with respect to the tire circumferential direction. Steel cords are exemplified as the cords constituting the belt 5, but organic fiber cords as described above can also be used.

  FIG. 2 conceptually shows the arrangement of the cords constituting the belt 5. Reference numeral W denotes a belt width. In FIG. 2, only half of the belt 5 is shown. The solid line extending obliquely is the cord 5c, and the broken line is a virtual line when the cord angle is constant. The mediate region Me is a region that is 50 to 80% of the belt width W around the tire equator line C. The inner region in the tire width direction is the center region Ce and the outer region in the tire width direction is the shoulder. It is set as area | region Sh. The end of the belt 5 is disposed in the shoulder region Sh.

  In the present invention, regarding the cord angle of the belt 5 with respect to the tire circumferential direction, when the cord angle in the mediate region Me is θm, the cord angle in the center region Ce is θc, and the cord angle in the shoulder region Sh is θs, θc> θs> The relationship of θm is satisfied. That is, the cord angle of the belt 5 (in this specification, the angle with respect to the tire circumferential direction unless otherwise specified) is minimum in the mediate region Me, maximum in the center region Ce, and intermediate in the shoulder region Sh. Is set as follows.

  According to such a configuration, the binding force of the belt 5 becomes the highest in the mediate region Me in which the inner surface shape of the tire tends to change locally. In addition, by making the cord angle of the shoulder region Sh smaller than the center region Ce, it is possible to uniformly suppress the diameter growth over the entire tire width direction. In addition, since the cord angle of the belt 5 can be set to be relatively large in the shoulder region Sh, an increase in distortion at the end of the belt 5 can be suppressed and excellent belt durability can be exhibited.

  FIG. 3 is a graph conceptually showing the transition of the cord angle of the belt 5. The horizontal axis is the distance in the tire width direction from the tire equator line C, and the vertical axis is the cord angle of the belt 5 with respect to the tire circumferential direction. As shown in this graph, the cord angle of the belt 5 gradually decreases from the center region Ce toward the mediate region Me, shows a minimum value in the mediate region Me, and from the mediate region Me to the shoulder region Sh. It is getting bigger gradually.

  Thus, when the chord angle changes in each area, the minimum chord angle value in the mediate area Me is θm, the maximum chord angle value in the center area Ce is θc, and the maximum chord angle in the shoulder area Sh is The value may be set to θs so that they satisfy the relationship θc> θs> θm. In the present embodiment, θc is obtained near the tire equator line C, and θs is obtained near the end of the belt 5.

  Therefore, the present invention includes a belt in which the cord angle changes as shown in FIG. (A) is an example in which the chord angle is constant in the mediate area Me, and (B) is an example in which the chord angle is also constant in the center area Ce. (C) is an example in which the chord angle is constant in the mediate region Me and in the vicinity of the mediate region Me in the center region Ce and the shoulder region Sh. In any of the cases (A) to (C), the relationship θc> θs> θm is satisfied.

  In the present invention, it is preferable to gradually change the cord angle of the belt 5 from the mediate region Me toward the center region Ce while satisfying the relationship of θc−θm ≦ 5 °. As a result, as shown in FIG. 2, the cord 5c can be smoothly arranged without being bent, and the strength of the belt 5 can be ensured appropriately. This is particularly useful when the cord 5c is a steel cord.

  In the present invention, 0 ° <θc−θm, preferably 2 ° <θc−θm, and more preferably 3 ° ≦ θc−θm. As a result, the cord angle in the mediate region Me is reliably reduced and the restraining force is relatively increased, so that the diameter growth can be more uniformly suppressed over the entire tire width direction.

  In the present invention, it is preferable that the cord angle of the belt 5 is gradually changed from the mediate region Me toward the shoulder region Sh while satisfying the relationship of θs−θm ≦ 3 °. As a result, as shown in FIG. 2, the cord 5c can be smoothly arranged without being bent, and the strength of the belt 5 can be ensured appropriately. This is particularly useful when the cord 5c is a steel cord.

  In the present invention, 0 ° <θs−θm, preferably 1 ° <θs−θm, and more preferably 2 ° ≦ θs−θm. As a result, the cord angle in the mediate region Me is reliably reduced and the restraining force is relatively increased, so that the diameter growth can be more uniformly suppressed over the entire tire width direction.

  In the present invention, 1 ° ≦ θc−θs is preferable, and 1.5 ° ≦ θc−θs is more preferable. As a result, the binding force of the belt 5 in the shoulder region Sh that tends to be lower than the center region Ce can be increased, and the diameter growth can be more uniformly suppressed over the entire tire width direction.

  Although FIG. 2 is conceptually described, the actual chord angle is generally smaller. Specifically, those in which θc is 10 to 30 °, θs is 8 to 28 °, and θm is 5 to 25 ° are exemplified. Further, as in the present embodiment, when the cord 5c is gently bent and has a portion that is not arranged linearly, the cord angle can be measured using a tangent.

  In FIG. 1, for convenience of illustration, the belt 5 is illustrated as a single-layer member, but actually, the belt 5 is configured by laminating a plurality of (for example, two, four) belt plies. . Each belt ply is disposed such that the cord angles cross in opposite directions between the plies, and the cord angles satisfy a relationship of θc> θs> θm. When the belt ply width dimensions are different from each other, the maximum width of the belt 5 is used as the belt width W.

  The setting of the cord angle as described above may be adopted for any of a plurality of belt plies constituting the belt, may be adopted for all belt plies, but is adopted for a belt ply that functions as a working belt. It is preferable. For example, in the case of pneumatic tires used in heavy-duty vehicles such as trucks and buses, when equipped with a belt formed by laminating four belt plies, the second and third belt plies that function as working belts are used. It is preferable to adopt.

  The present invention is particularly useful for tires having a flatness ratio (tire cross section height / tire cross section width × 100) of 70% or less, and more useful for tires having a flat ratio of 60% or less. In such a tire having a low flatness ratio, the length of the carcass 4 in the sidewall portion 2 is relatively short, and the bulge to the outside in the tire width direction is suppressed, and the change in the inner surface shape in the mediate region Me is remarkable. Therefore, the configuration of the present invention is particularly useful.

  The pneumatic tire of the present invention exhibits excellent belt durability while suppressing diameter growth due to the above-described effects, and is useful as a heavy duty pneumatic tire used under high internal pressure and high load. Useful as a super single tire. A super single tire is an ultra-flat tire obtained by combining two single-wheel tires that have conventionally been two on one side in trucks and buses.

  The pneumatic tire of the present invention can be manufactured in the same manner as in the conventional tire manufacturing process, with modifications to such an extent that the cord angle of the belt is set as described above. The belt as described above is arranged, for example, by using the manufacturing apparatus described in Japanese Patent Application Laid-Open No. 2002-127711 filed by the applicant of the present invention, one by one or several at a time and changing the cord angle. It can produce by doing.

  Examples that specifically show the structure and effects of the present invention will be described below. Evaluation items in Examples and the like were measured as follows.

(1) Diameter growth (internal stability)
For tires of size 445 / 50R22.5, the inner diameter was measured in three states, rim gathering, new INF and grown INF, and the inner surface state between each state was evaluated. The measurement position of the inner diameter was set at 10 mm intervals in the tire width direction from the tire equator line to the end of the belt. In Table 1 and FIG. 5 to be described later, the amount of inner surface change (diameter growth amount) from the time of rim alignment to the time of INF after growth is listed. However, Table 1 shows the values at the representative positions of each region, and the representative positions of the center, mediate, and shoulder regions are 0, 78, and 100% of the distance from the tire equator line to the belt half width, respectively. The position is set.

  Note that rim gathering refers to a state in which a new tire assembled with a rim is slightly filled with air and the internal pressure is 50 kPa. The new INF refers to a state in which the tire in the rim-shifted state is further filled (inflated) with air and the internal pressure is set to 830 kPa. Further, the post-growth INF refers to a state in which a tire in a new INF state is run for 20000 km at 88 km / h on a drum and then the internal pressure is set to 830 kPa. The evaluation results of each example are shown in Table 1 and FIG.

(2) Belt durability Using a tire having a size of 445 / 50R22.5, drum running was performed according to the durability test of ECE54, and the running distance until the belt failed was evaluated. The result of the conventional example is shown as an index with 100, and the larger the value, the better the belt durability. The evaluation results of each example are shown in Table 1.

  From Table 1 and FIG. 5, it can be seen that in Examples 1 and 2, the diameter growth is suppressed, the inner surface is stable, and excellent belt durability is exhibited. On the other hand, in Comparative Example 1, the shoulder region is drawn inward, the inner surface is not stable, and the belt durability is low. In Comparative Example 2, diameter growth is large in the shoulder region, and belt durability is low. In Comparative Examples 3 and 4, the effect of suppressing the diameter growth is small, and in the conventional example, the suppression of the diameter growth is insufficient and the belt durability is low.

  FIG. 6 is a schematic diagram showing changes in the cross-sectional shape of the tire in (A) a conventional example and (B) Example 1. A solid line indicates a rim approach, a one-dot chain line indicates a new INF, and a two-dot chain line indicates a state of INF after growth.

  In the conventional example, in the process from the rim gathering to the new INF, and further in the process from the new INF to the grown INF, the diameter growth is large over the entire tire width direction. On the other hand, in Example 1, the diameter growth in the process from the rim gathering to the new INF is slight, and the diameter growth is well suppressed in the process from the new INF to the post-growing INF, and the inner shape of the tire Is stable.

The tire meridian half sectional view schematically showing an example of the pneumatic tire according to the present invention Conceptual diagram showing belt cord arrangement Graph showing changes in belt cord angle The graph which shows transition of the cord angle of the belt in another embodiment of the present invention. Graph showing the amount of internal growth Schematic diagram showing changes in the cross-sectional shape of the tire in the conventional example and Example 1 Conceptual diagram showing belt cord arrangement in conventional tires Diagram explaining tire behavior in the process of radial growth

Explanation of symbols

2 Side wall part 4 Carcass 5 Belt 5c Code C Tire equator line Ce Center area Me Mediate area Sh Shoulder area W Belt width

Claims (4)

In a pneumatic tire provided with a belt arranged so that the cord is inclined with respect to the tire circumferential direction,
An area that is 50 to 80% of the belt width centered on the tire equator line is a mediate area, an area inside the tire width direction from the mediate area is a center area, and an area that is outside the mediate area in the tire width direction Is the shoulder area,
Regarding the cord angle with respect to the tire circumferential direction of the belt, when the cord angle in the mediate region is θm, the cord angle in the center region is θc, and the cord angle in the shoulder region is θs,
A pneumatic tire characterized by satisfying a relationship of θc>θs> θm.   The pneumatic tire according to claim 1, wherein the cord angle of the belt is gradually changed from the mediate region toward the center region while satisfying a relationship of θc−θm ≦ 5 °.   3. The pneumatic tire according to claim 1, wherein the cord angle of the belt is gradually changed from the mediate region toward the shoulder region while satisfying a relationship of θs−θm ≦ 3 °.   The pneumatic tire according to any one of claims 1 to 3, wherein the flatness is 70% or less.

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